US ambassador to South Korea Mark Lippert underwent two-and-a-half hours of surgery after he was slashed in the face by a Korean nationalist in an attack at a forum held in Seoul on Thursday to discuss Korean reunification, officials said.

Mr Lippert, 42, was bleeding from wounds to his face and wrist but was able to walk after the attack.

Doctors said they treated Lippert for an 11cm (4ins) gash on the right side of his face and a puncture wound on his left wrist, causing nerve damage that was repaired. He will be hospitalised for three or four days, they said.

Despite the attack, Mr Lippert said he was well and in great spirits as he recovered from surgery to treat wounds on his face and arm:

Doing well&in great spirits! Robyn, Sejun, Grigsby & I – deeply moved by the support! Will be back ASAP to advance US-ROK alliance! ê°?ì´ ê°?ì??ë?¤!

The assailant was caught and identified by police as 55-year-old Kim Ki-jong. In 2010, Kim tried to attack the Japanese ambassador to Seoul by throwing a piece of concrete and was given a suspended jail term, according to police.

Witnesses and police said Kim used a small fruit knife in the attack, which took place inside a large government arts centre across the street from the heavily guarded US embassy on the South Korean capital’s main ceremonial thoroughfare.

“I carried out an act of terror,” Kim shouted as he was pinned to the floor by people at the event.

“We strongly condemn this act of violence,” US State Department spokeswoman Marie Harf said. President Obama called Lippert to wish him a speedy recovery, a White House official said.

North Korea’s official KCNA news agency called the attack “deserved punishment” for US military exercises with South Korea, calling the assault “the knife of justice”.